Since the early 1970's, digital communicators have been in increasing use for reporting alarm or status conditions to central monitoring stations. The digital communicators, which use a digital stream of data to denote the reporting account number and status code, improve upon the previously used tape dialers which utilize a tape recorded message to identify the calling location.
As digital communicators evolved, the digital stream of data acquired different formats. A number of models are designed for pulsed transmissions at slow rates of 10 pulses per second. Faster pulsed rates, at 20 pulses per second, came in vogue when the need to conserve line capacity and to speed the handling of alarms became evident. It was found however in some locations that due to noise and other degradations in the transmission medium, the faster pulse rate was less reliable than the slow pulse rate. This led to the manufacture of transmitters with "Touch-Tone" (Touch-Tone is a trademark of AT&T), generically known as DTMF (Dual Tone Multiple Frequency), formats which combine super fast transmission with high reliability. For example, 15 distinct pulses are required in the pulsed formats to transmit the letter F, whereas only one DTMF pair is required for any hexadecimal symbol.
Each of the different transmission formats requires a given protocol between transmitter and receiver. This protocol consists of frequency coded handshake signals and kiss-off signals. The handshake signal is emitted by the receiver to initiate transmission of data by the transmitter. The kiss-off signal is emitted by the receiver to signal that data has been received correctly. The presence of the handshake and kiss-off signals at appropriate times is necessary for communications. Because the various formats require different kiss-off and handshake signals, it has been required in the past to segregate transmitters of different formats onto separate communication lines. This invention permits mixing of different formats on the same communications line.
When several reports are received within a short interval of time, the operator needs to note each arriving report as it is displayed on the receiver. For each report different operator action may be required. The action is often of urgent nature, such as a call for help to police, fire department, ambulance or other emergency service. Because of the possibility of human error, busy periods may result in failure to service alarms. This invention describes means to store and display the arriving data so as to provide the operator with an organized display. The organization described in this invention ensures that each received call is serviced by the operator. When the operator takes action on a received call, notation of the action in a log is required. With past equipment, the action log is often kept in a notebook separate from the receiver and with date and time independently entered. This invention describes means to enter the action log into the receiver and of permanently storing the action log with date and time automatically entered by the receiver. This improvement results in the joint storage of received messages and the resulting action log.
A further improvement relates to reception of analog data in combination with receptions from digital communicators. In the past, separate modems and receivers from the receiver used to acquire digital alarms were needed for analog data. The improved receiver allows analog information, the precise value of a parameter, as well as digital data to be received.
A further improvement relates to the automatic handling of messages which normally arrive at predetermined times. Examples of such messages are reports of openings and closings of commercial businesses. Past procedure has been to track these calls manually. This usually involves punching time cards for each account by the operator. This procedure is time consuming and error prone. This invention describes automatic tracking of normal events such as openings and closings. The receiver signals distinctly when a call arrives due to a normal event, when a call arrives outside its expected time slot, and the failure of an expected message to arrive.
Another feature of this improvement is the monitoring by the receiver of faulty or disconnected transmitters. This invention applies to automated monitoring of transmitters programmed to report at least once within a prescribed interval, for example once a day. The invention gives a distinct indication when it fails to receive a message from a transmitter in its assigned interval.